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The present invention relates to control systems and apparatus for selectively supplying electrical power in a remote environment. More particularly, the invention relates to systems and apparatus for remotely filtering power through one or more electrical circuits located downhole in oil and gas wells to selectively power a device proximate the electrical circuit.
In the operation of electrically powered equipment, systems and apparatus are sometimes employed to operate the equipment in remote and hostile environments. For example, in the operation of hydrocarbon wells, the production of hydrocarbons to the surface of the well at times requires the assistance of downhole production systems. Generally, after a well is drilled, cased and cemented, a fluid path from the wellbore is established with the zones of reservoirs containing hydrocarbons. One or more production tubing strings are traditionally installed in the cased wellbore to accommodate the flow of hydrocarbons to the surface. While hydrocarbons from some reservoirs flow through the production tubing to the surface relatively unassisted, other reservoirs require the assistance of production systems which are installed downhole. Such production equipment is traditionally coupled to the tubing string.
One type of production system is a gas lift operation that includes a valve system for controlling the injection of relatively high pressure gas from the surface into the wellbore. The pressurized gas is injected into the annular space between the casing and tubing and enters the tubing through downhole gas lift valves. The gas lifts the fluids that are collecting in the tubing to assist the flow of hydrocarbon fluids to the surface. Gas injection into the well thus requires the operation of the downhole gas lift valve to control the injection gas flow. The gas lift valves are strategically positioned along the production tubing string in relatively close proximity to the hydrocarbon laden zones. The valves are normally closed to restrict the flow of injection gas from the casing into the tubing and are opened to allow the flow of injection gas into the tubing. Generally, gas lift valves are hydraulically operated. By controlling the flow of a hydraulic fluid, a downhole hydraulic valve is actuated to control the flow of fluid into the gas lift valve. The gas lift valve is moved from a closed to an open position for as long as necessary to affect the flow of the pressurized gas from the casing into the tubing. Such gas lift valves are position instable. Upon interruption of the hydraulic control pressure, the gas lift valve returns to its normally closed configuration.
In a gas lift system, there is a requirement for the periodic operation of a motor valve at the surface of the well to control either the flow of fluids from the well or the flow of injection gas into the well to assist in the hydrocarbon production. These motor valves are controlled by timing mechanisms and are set at predetermined time periods so that a well is either restricted from the flow of gas or liquids to the surface or is allowed to freely produce.
It will be appreciated that timed intermittent operation of motor valves and similar devices located at the surface of a well is often not adequate to control either outflow from the well or gas injection to the well so as to optimize well production. Computerized controllers have thus been developed for controlling downhole production equipment. In general, there are control systems that use a surface microprocessor and downhole control systems which are initiated by surface control signals. The control electronics of these computerized systems are located at the surface of a well and communicate with sensors and electromechanical devices near the surface. For example, some systems include fully programmable microprocessor controllers which monitor downhole parameters such as pressure and flow and control the operation of gas injection to the well, outflow of fluids from the well or shutting in of the well. These systems may include battery powered solid state circuitry comprising a keyboard, a programmable memory, a microprocessor, control circuitry and a liquid crystal display. Other systems use a controller having serial and parallel communication ports through which all communications to and from the controller pass. Hand held devices or portable computers capable of serial communication may access the controller. A telephone modem or telemetry link to a central host computer may also be used to permit several controllers to be accessed remotely.
Downhole control systems generally include downhole microprocessor controllers, electromechanical control devices and sensors. For example, some downhole microprocessor controllers transmit control signals upon actuation from a surface or other external control signal. Other production well control systems comprise downhole sensors, downhole electromechanical devices and downhole computerized control electronics wherein the control electronics automatically control the electromechanical devices based on input from the downhole sensors. The downhole computerized control system will monitor actual downhole parameters such as pressure, temperature, flow and gas influx, all sensed by the downhole sensors, and automatically execute control instructions when the monitored downhole parameters are outside a selected operating range. The automatic control instructions will then cause an electromechanical control device such as a valve to actuate the appropriate tool. The selected operating range for each tool controlled by the downhole control system is programmed in a downhole memory either before or after the control system is lowered downhole. A transceiver may be used to change the operating range or alter the programming of the control system from the surface of the well or from a remote location. A power source provides energy to the downhole control system. Power for the power source can be generated in the borehole, at the surface or via energy storage devices such as batteries, or a combination thereof. The power source provides electrical voltage and current to the downhole electronics, electromechanical devices and sensors in the borehole.
While it is recognized that hydrocarbon production wells will have increased production efficiencies and lower operating costs if surface computer based controllers and downhole microprocessor controllers are used, the implemented control systems of the prior art nevertheless have certain drawbacks. In particular, the controllers of such systems include complex circuitry that is sensitive to environment conditions such as pressure and temperature. The downhole circuitry would thus require containment in canisters capable of withstanding hostile conditions that are present in downhole environments. In addition, the substantial numbers of components which comprise the microprocessors create reliability, repair and maintenance issues which are relatively expensive to address, as the downhole circuitry would have to be removed from the well in order to be repaired or replaced.
While the control system and apparatus of the present invention are discussed in the context of a downhole environment, it will be appreciated that the present invention is also application to other systems which require operation in remote and hostile conditions.
Through significant time and effort, it has been found that the difficulties associated with microprocessors could be avoided by the control system of the present invention that uses relatively simple electrical circuitry. As will be appreciated by one skilled in the art, the novel apparatus and control system of the present invention are applicable to other types of equipment other than downhole equipment for which remote operation is desired. The control system comprises electrical circuits of frequency selecting units having discrete frequency passbands for selectively filtering power to corresponding devices, either individually or simultaneously with other frequency selecting units. Thus the control system of the present invention is well suited and designed for use in connection with wells having multiple hydrocarbon zones.
The frequency selecting units of the electrical circuits have inductance and capacitance characteristics which define their frequency passbands. Power transmitted at a frequency within a discrete frequency passband is filtered through the electrical circuit of the frequency selecting unit corresponding to the passband. Alternatively, power can be transmitted at frequencies within a plurality of frequency passbands for filtering through multiple frequency selecting units in a multi-unit system to selectively and simultaneously power a plurality of devices corresponding to the frequency selecting units. The apparatus and systems described herein have allowed for electrical components that traditionally do not have severe pressure and temperature limitations and thus can withstand relatively hostile conditions that may be found downhole or in other remote environments. In addition, the control system and apparatus of the present invention is reliable and robust as it comprises relatively few components.
The power source which supplies the electrical power to the control system of the present invention can be proximate any desired location. For example, the source can be proximate the surface of the well, located downhole or in a remote area. In addition, the power source can be variable frequency or multiple frequencies so long as the power is transmittable within the frequency passbands of the frequency selecting units of the present invention. Further, DC power may also be appropriate.
The inductance and capacitance characteristics of the frequency selecting units can be provided by any suitable component, such as, for example, inductors and capacitors. In addition, the inductance or capacitance could be supplied by a reactive electromotive device such as a motor, a solenoid or a piezoelectric device. As the power frequency range for each frequency selecting unit depends on at least the inductance or capacitance rating of the frequency selecting unit, each unit can be uniquely designed to filter power within a discrete frequency passband. Different inductance and capacitance values for each frequency selecting unit can be used to achieve discrete frequency passbands. Similar inductance but different capacitance characteristics could also be used for each unit to achieve the discrete frequency passbands. Alternatively, different inductance but similar capacitance characteristics for each frequency selecting unit could also be used. Further, the inductance and capacitance components of the frequency selecting unit can be in series or in parallel to create the discrete passbands. Thus, by transmitting power within a selected discrete frequency passband, a device corresponding to the frequency selecting unit that filters power within that passband can be powered. Power can also be transmitted within a plurality of frequency passbands to selectively and simultaneously power a plurality of devices corresponding to the filtering frequency selecting units.
The devices which can be selectively powered by using frequency selecting units which filter power through an electrical circuit include without limitation batteries, sensors and telemetry. In addition, actuable devices can be powered by certain frequency selecting units which not only filter power but also convert an electrical current into a force to operate the actuable device. For example, a solenoid would provide not only the inductance of the frequency selecting unit but could also operate to open or close a gas lift valve or other actuable device. Other examples include motors and other electric actuators. In addition, a piezoelectric device would provide the capacitance of the frequency selecting unit and would also operate the actuable device. Thus, in an embodiment of the present invention, frequency selecting units selectively filter power through a corresponding electrical circuit to actuate devices proximate the units.
In another embodiment of the present invention, the electrical circuits of the control system are designed to accommodate a frequency-shifting characteristic which is inherent in certain types of frequency selecting units. For example, the frequency-shifting characteristic of a solenoid comprises a change in the inductance of the solenoid as it moves from its initial actuation through its stroke. In other frequency selecting units, the inductance rating may change during its initial powering through its continued operation. The frequency band width allocated to each frequency selecting unit should be sufficiently broad to accommodate the frequency shift so that the unit is continually powered for uninterrupted operation. However, minimal overlap of passbands between the frequency selecting units should be maintained in order to preserve the discreteness of the operable frequency passband for each frequency selecting unit.
Thus, a control system having frequency passbands which are sufficiently broad to accommodate the frequency shifting of the frequency selecting units yet which have minimal overlap with other passbands is desirable. A limitation to the system frequency band width design is the electrical conductor which transmits power downhole to the frequency selecting units. The electrical conductor inherently has frequency limitations which allow it to accommodate only a finite band width. Thus, it is advantageous to minimize the band widths for each frequency selecting unit so that the number of units for remote operation can be maximized. Accordingly, in another embodiment of the control system of the present invention, a single directional silicon controlled rectifier for direct current circuits or a bi-directional triac for alternating circuits is provided proximate one or more frequency selecting units. The rectifier and triac, so-called xe2x80x9cturn-on gates,xe2x80x9d filter power within the appropriate frequency passband to the frequency selecting unit. For example, the triac is a three terminal device that requires a small input of power to one of the terminals in order to create essentially a short between the other two terminals. The switch does not turn on until power input is supplied to the first terminal which then powers the frequency selecting unit proximate the switch. An advantage of the turn-on gate is the conservation of power to the other unused frequency selecting units, as these units would receive some amount of power, although not in an amount sufficient to operate the units. Conserving power minimizes the frequency band width required to operate the desired frequency selecting unit and continually power it. Thus, the turn-on gate circuit provides narrower discrete frequency passbands which allow more frequency selecting units on a single electrical conductor. The turn-on device advantageously allows only the selected frequency selecting units to receive power, while the other frequency selecting units receive essentially no power, thus minimizing the frequency dependent limitations inherent in the electrical conductor. Thus, by utilizing a triac turn-on gate with the frequency selecting units, a larger number of units can be controlled using the same electrical conductor downhole.
In yet another embodiment, a high temperature operational amplifier or op-amp could be used in a control system of the present invention for additional and effective filtering of power through the electrical circuits of the present invention. Each frequency selecting unit would have a uniquely rated op-amp such that power transmitted within the selected frequency passbands having a discrete current flow would power the corresponding frequency selecting units.
The invention is more particularly shown and described in the accompanying drawings and materials included herein.